Newer polymerization catalysts have the unique ability to produce polymers having product properties that have not been previously obtained. Those polymerization catalysts are typically expensive and highly sensitive to impurities in the feed streams. Impurities in the feed streams poison or otherwise affect the polymerization catalysts, thereby significantly decreasing the catalyst activity and performance. As such, the presence of impurities dramatically increases production costs and is a detriment to product quality. There is a need, therefore, for a cost-effective way to remove impurities in the feed streams prior to polymerization.
Processes that polymerize olefins, for example, ethylene, propylene, butene, hexene, octene, etc. often use high-activity catalysts that may be sensitive to poisons in the polymerization feed stream. Common poisons that decrease catalyst activity or cause operating problems in the polymerization process include, among others, oxygen (O2) and carbon monoxide (CO). Copper (Cu) in its various oxidation states, particularly copper oxide (CuO), is useful for removing certain poisons, such as carbon monoxide, through catalytic oxidation of carbon monoxide to carbon dioxide (CO2). However, the oxidation of carbon monoxide by copper oxide is typically accomplished at temperatures well above ambient temperature to effectively remove the carbon monoxide. For example, a review in Katz, Morris, “Heterogeneous Oxidation of Carbon Monoxide,” in Advances in Catalysis, vol. V, p. 177 (1953), indicates that the oxidation of carbon monoxide by unpromoted copper oxide may not commence until about 200° C. (392° F.).
Purification processes may require heating and cooling the feed olefin to effectively remove the catalyst poisons from the olefin feed, thus, consuming significant energy to process the feed olefin. For example, a reactor system may receive olefins at about ambient temperatures—e.g., about 0° C. (32° F.) to about 35° C. (95° F.). The olefin purification train has individual stages for removal of oxygen and carbon monoxide followed by a vessel having an adsorbent bed(s) for removal of water and carbon dioxide. The oxygen and carbon monoxide removal beds typically operate at about 100° C. (212° F.) or higher, while the adsorbent beds typically operate at ambient temperatures. This means the feed olefin must first be heated to 100° C. (212° F.) or higher prior to oxygen removal then cooled again to near-ambient temperatures thereafter and prior to contacting the adsorbent bed(s).
One catalyst known for removing carbon monoxide is a mixture of copper oxide and manganese dioxide known as hopcalite. Some hopcalite catalysts are thought to remove carbon monoxide from dry air by reaction at ambient temperature as low as −20° C. (−4° F.). U.S. Pat. No. 2,837,587 discusses the removal of carbon monoxide from a mixture of olefins and hydrogen at about 10° C. (50° F.) to about 90° C. (194° F.) and at space velocity up to about 1000 h−1 with a hopcalite catalyst. However, hopcalite may hydrogenate some olefins, such as ethylene, making it undesirable for many polyolefin polymerization processes.
U.S. Pat. No. 5,907,076 discloses a copper oxide catalyst to oxidize hydrogen and carbon monoxide contained in a hydrocarbon stream at a temperature as low as about 40° C. (104° F.). The Examples of the '076 patent demonstrate an oxidation temperature of about 104° C. (219° F.). The '076 patent indicates multiple scenarios of operation. In one scenario, the carbon monoxide is reacted with less than a stoichiometric amount of oxygen, which results in little oxygen passing through the removal bed, but some carbon monoxide passing through the removal bed. In a subsequent step, the remaining carbon monoxide is removed by reacting carbon monoxide and water over a separate metal oxide catalyst to form carbon dioxide. In another scenario, the stream is denuded of carbon monoxide by reacting the carbon monoxide with a copper oxide catalyst with 100% to 500% of the stoichiometric amount of oxygen present, but allows for oxygen passing through the removal bed.
EP 0 966 508 A discusses a process comprising at least two steps for removing impurities, such as oxygen, in an olefin stream. The first step teaches the hydrogenation of oxygen and other impurities using a hydrogenation catalyst containing silver and palladium. The second step teaches removing at least part of the residual oxygen by oxidation with carbon monoxide with a copper/copper oxide catalyst. The disclosure indicates that during the reaction of carbon monoxide and oxygen, the temperature should be at least about 15° C. (59° F.) and preferably about 40° C. (104° F.) or more.
Other background references include U.S. Pat. Nos. 3,676,516; 4,025,321; 4,233,038; 4,784,672; 5,157,204; 5,447,558; 6,069,288; 6,124,517; 6,168,769; 6,680,419; 6,987,152; 7,314,965; U.S. Application Nos. 2003/0105376; 2003/0105379; 2003/0200866; 2004/0045434 and WO 2006/076096.